Heat exchanger

ABSTRACT

An evaporator ( 11 ) is provided that carries out heat exchange between exhaust gas discharged from an exhaust port ( 16 B) of an internal combustion engine and water, the evaporator ( 11 ) including a large number of heat transfer plates ( 83 ) stacked at predetermined intervals from each other in a direction perpendicular to the plane of the paper and a large number of pipe members ( 90 ) running through the heat transfer plates ( 83 ) and being connected in a zigzag shape at opposite ends, and exhaust gas passages ( 87, 88, 89 ) being defined between the heat transfer plates ( 83 ) by a partition wall ( 86 ) formed by making projections formed on the heat transfer plates ( 83 ) abut against each other. While passing through the exhaust gas passages ( 87, 88, 89 ), the exhaust gas discharged from the exhaust port ( 16 B) carries out heat exchange with water flowing through the pipe members ( 90 ), and the water that has received the thermal energy of the exhaust gas turns into high temperature, high pressure steam. It is thus possible to maximize the heat transfer area of the evaporator ( 11 ) and thereby improve the heat exchange efficiency.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger for recovering, with aheat medium flowing through a heat medium passage, the thermal energy ofa high temperature fluid flowing through the interior of a fluid passageextending from a heat source.

BACKGROUND ART

An evaporator that carries out heat exchange between exhaust gas of aninternal combustion engine and water so as to heat the water by the heatof the exhaust gas and generate high temperature, high pressure steam isknown from Japanese Patent Application Laid-open Nos. 2001-207910 and2001-207839.

Japanese Patent Application Laid-open No. 2001-207910 discloses anarrangement in which an evaporator is disposed in each of a plurality ofexhaust ports of a multicylinder internal combustion engine, thus givinga high efficiency of heat exchange with a high temperature exhaust gaswhile avoiding the occurrence of exhaust interference and therebyensuring the output of the internal combustion engine, and a singleevaporator is disposed in a section where a plurality of exhaustpassages are combined, thereby improving the efficiency of heat exchangeby using exhaust gas that has decreased pulsations after being mergedand thus has a uniform temperature. Japanese Patent ApplicationLaid-open No. 2001-207839 discloses an arrangement in which a pluralityof heat exchangers are disposed in a layered state in an exhaust passageof an internal combustion engine, thus lowering the heat transferdensity of a heat exchanger on the upstream side where the flow rate ofexhaust gas is high and increasing the heat transfer density of a heatexchanger on the downstream side where the flow rate of exhaust gas islow, and thereby ensuring a uniform heat transfer performance across allof the heat exchangers.

However, since the above-mentioned conventional heat exchanger has astructure in which heat exchange is carried out by contacting theexhaust gas with the external surface of a spiral- or zigzag-shaped pipemember within which water flows, the heat transfer area is limited tothe surface area of the pipe member, and there is a limit to theimprovement of the heat exchange efficiency.

DISCLOSURE OF INVENTION

The present invention has been achieved under the above-mentionedcircumstances, and it is an object thereof to improve the heat exchangeefficiency by maximizing the heat transfer area of a heat exchanger.

In order to attain this object, in accordance with a first aspect of thepresent invention, there is proposed a heat exchanger for recovering,with a heat medium flowing through a heat medium passage, the thermalenergy of a high temperature fluid flowing through the interior of afluid passage extending from a heat source, characterized in that thefluid passage is formed by arranging a large number of heat transferplates at intervals from each other and partitioning the gaps betweenadjacent heat transfer plates using a partition wall that is formedintegrally with the heat transfer plates, and the heat medium passage isformed from a large number of pipe members running through the heattransfer plates and being connected in a zigzag shape.

In accordance with this arrangement, since the fluid passage is formedby partitioning, using the partition wall, the gaps between the largenumber of heat transfer plates arranged at intervals from each other,and the heat medium passage is formed by the large number of pipemembers running through the heat transfer plates and being connected ina zigzag shape, it is possible to carry out heat exchange between theexhaust gas and the heat medium via the large surfaces of the largenumber of heat transfer plates and the large number of pipe members,thereby greatly improving the heat exchange efficiency. Moreover, sincethe partition wall partitioning the gaps between adjacent heat transferplates is formed integrally with the heat transfer plates, a fluidpassage having any shape can be constructed with a simple structurewhile suppressing any increase in the number of components.

Furthermore, in accordance with a second aspect of the presentinvention, in addition to the first aspect, there is proposed a heatexchanger wherein the packing density of the pipe members disposed onthe upstream side of the fluid passage is sparse and the packing densityon the downstream side of the fluid passage is dense.

In accordance with this arrangement, since the packing density of thepipe members disposed on the upstream side of the fluid passage issparse and the packing density of the pipe members disposed on thedownstream side of the fluid passage is dense, it is possible to reducethe pressure loss caused by the pipe members on the upstream side of thefluid passage, where the flow rate is high because the high temperaturefluid has high temperature and a large volume, and it is possible toensure the efficiency of heat exchange between the heat medium and thehigh temperature fluid on the downstream side of the fluid passage,where the flow rate is low because the high temperature fluid has lowtemperature and a small volume.

Moreover, in accordance with a third aspect of the present invention, inaddition to the first or second aspect, there is proposed a heatexchanger wherein the heat source is a combustion chamber of an internalcombustion engine, the high temperature fluid is exhaust gas dischargedfrom the combustion chamber, and the heat transfer plates support anexhaust gas purification catalyst.

In accordance with this arrangement, since the exhaust gas purificationcatalyst is supported on the heat transfer plates, when the exhaust gasdischarged from the combustion chamber of the internal combustion enginecarries out heat exchange with the heat medium via the heat transferplates, the exhaust gas can be cleaned up by the exhaust gaspurification catalyst. Moreover, since the heat transfer platessupporting the exhaust gas purification catalyst have a large surfacearea, the exhaust gas purification efficiency can be increased.

A combustion chamber 24 of an embodiment corresponds to the heat sourceof the present invention, first to third exhaust gas passages 87, 88,and 89 of the embodiment correspond to the fluid passages of the presentinvention, and a water passage W3 of the embodiment corresponds to theheat medium passage of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 to FIG. 23 show one embodiment of the present invention; FIG. 1is a diagram showing the overall arrangement of a Rankine cycle system;FIG. 2 is a vertical sectional view of the surroundings of a cylinderhead of an internal combustion engine; FIG. 3 is an enlarged view of apart 3 in FIG. 2; FIG. 4 is a view from arrowed line 4-4 in FIG. 2; FIG.5 is a sectional view along line 5-5 in FIG. 4; FIG. 6 is a sectionalview along line 6-6 in FIG. 4; FIG. 7 is a partially cutaway perspectiveview of an independent exhaust port; FIG. 8 is a view from arrow 8 inFIG. 7; FIG. 9 is a view from arrow 9 in FIG. 8; FIG. 10 is a view fromarrow 10 in FIG. 8; FIG. 11A and FIG. 11B are schematic views showingthe flow of water in a grouped exhaust port; FIG. 12 is an enlargedsectional view of an essential part in FIG. 2; FIG. 13 is a view fromarrowed line 13-13 in FIG. 12; FIG. 14 is a view from arrow 14 in FIG.12; FIG. 15 is a sectional view along line 15-15 in FIG. 12; FIG. 16 isan enlarged view of a part 16 in FIG. 15; FIG. 17 is a sectional viewalong line 17-17 in FIG. 14; FIG. 18 is a sectional view along line18-18 in FIG. 14; FIG. 19 is a sectional view along line 19-19 in FIG.14; FIG. 20 is a sectional view along line 20-20 in FIG. 12; FIG. 21 isa sectional view along line 21-21 in FIG. 12; FIG. 22 is a diagramshowing the flow of water in a main evaporator; and FIG. 23 is a diagramshowing the flow of exhaust gas in the main evaporator.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is explained below with referenceto FIG. 1 to FIG. 23.

FIG. 1 shows the overall arrangement of a Rankine cycle system to whichthe present invention is applied.

The Rankine cycle system, which recovers the thermal energy of anexhaust gas of an internal combustion engine E and converts it intomechanical energy, includes a main evaporator 11 that heats water withexhaust gas discharged from the internal combustion engine E so as togenerate high temperature, high pressure steam, an expander 12 that isoperated by the high temperature, high pressure steam generated by themain evaporator 11 so as to generate mechanical energy, a condenser 13that cools decreased temperature, decreased pressure steam that hascompleted work in the expander 12 so as to turn it back into water, areservoir tank 14 for collecting water discharged from the condenser 13,and a supply pump 15 for pressurizing the water collected in thereservoir tank 14. A portion of the water discharged from the supplypump 15 is supplied to the main evaporator 11, which is provideddownstream of an exhaust port 16 of the internal combustion engine E,turns into high temperature, high pressure steam in the main evaporator11, and is supplied to the expander 12, and the rest of water dischargedfrom the supply pump 15 is heated while passing through an auxiliaryevaporator 17 provided on the outer periphery of the exhaust port 16,and then merges into the main evaporator 11 at a predetermined position.

The main evaporator 11 carries out heat exchange mainly with the exhaustgas discharged from the exhaust port 16 and generates steam, but theauxiliary evaporator 17 carries out heat exchange not only with theexhaust gas flowing through the exhaust port 16 but also with theexhaust port 16 itself, which is in contact with a high temperatureexhaust gas, thus generating steam and simultaneously cooling theexhaust port 16.

As shown in FIG. 2, a cylinder head 20 and a head cover 21 are joined toa cylinder block 19 of the in-line four-cylinder internal combustionengine E, and four combustion chambers 24 are formed between the lowerface of the cylinder head 20 and the upper face of each of four pistons23 slidably fitted in four cylinder sleeves 22 housed in the cylinderblock 19. Formed in the cylinder head 20 are intake ports 26 and exhaustports 16, which communicate with the corresponding combustion chambers24. An intake valve seat 27 at the downstream end of the intake port 26is opened and closed by a head 28 a of an intake valve 28, and anexhaust valve seat 29 at the upstream end of the exhaust port 16 isopened and closed by a head 30 a of an exhaust valve 30. Whereas theintake port 26 is formed directly in the cylinder head 20, the exhaustport 16 is formed from four independent exhaust ports 16A and onegrouped exhaust port 16B, each thereof being made of a member that isseparate from the cylinder head 20 and fitted in the cylinder head 20.

Supported on the cylinder head 20 are a single camshaft 31, a singleintake rocker arm shaft 32, and a single exhaust rocker arm shaft 33.One end of an intake rocker arm 34 rockably supported by the intakerocker arm shaft 32 abuts against an intake cam 35 provided on thecamshaft 31, and the other end thereof abuts against a stem 28 b of theintake valve 28, which is slidably supported by an intake valve guide 36provided in the cylinder head 20 and is urged upward by a valve spring37. Furthermore, one end of an exhaust rocker arm 38 rockably supportedby the exhaust rocker arm shaft 33 abuts against an exhaust cam 39provided on the camshaft 31, and the other end thereof abuts against theupper end of a stem 30 b of the exhaust valve 30, which is slidablysupported by an exhaust valve guide 40 provided in the cylinder head 20and is urged upward by a valve spring 41.

The exhaust port 16 is formed from the four independent exhaust ports16A, which are positioned on the upstream side of the flow of exhaustgas, and the single grouped exhaust port 16B, which communicates withthe downstream side of the independent exhaust ports 16A, and an endportion on the upstream side of the main evaporator 11 is fitted intothe inside of the grouped exhaust port 16B. The auxiliary evaporator 17is provided so as to straddle the independent exhaust ports 16A and thegrouped exhaust port 16B communicating with the downstream side thereof.

The structure of the independent exhaust ports 16A is first explained indetail with reference to FIG. 3 and FIG. 7.

The independent exhaust port 16A is formed from a first port member 51,a first cover member 52, a second port member 53, and a second covermember 54. The first port member 51 and the first cover member 52 forman upstream portion 55 of the independent exhaust port 16A thatcommunicates with the combustion chamber 24, and have a structure inwhich the first port member 51, which is on the inside, is covered bythe first cover member 52, which is on the outside, and alabyrinth-shaped water passage W2 is formed between the inner face ofthe first cover member 52 and a channel formed on the outer face of thefirst port member 51. The lower faces of the first port member 51 andthe first cover member 52 abut against the upper face of the exhaustvalve seat 29, which is formed in the cylinder head 20, via a seal 56.Moreover, an opening 51 a through which the stem 30 b of the exhaustvalve 30 runs is formed in an upper wall of the first port member 51,and the lower end of the exhaust valve guide 40 is fitted via a seal 57in an opening 52 a formed on an upper wall of the first cover member 52.

The second port member 53 and the second cover member 54 form adownstream portion 58 of the independent exhaust port 16A, whichcommunicates with the grouped exhaust port 16B, and have a structure inwhich the second port member 53, which is on the inside, is covered bythe second cover member 54, which is on the outside, and thelabyrinth-shaped water passage W2 is formed between the inner face ofthe second cover member 54 and a channel formed on the outer face of thesecond port member 53. An end portion of the second cover member 54 isfitted in an opening 52 b formed in a side face of the first covermember 52, thereby joining the first port member 51 and the second portmember 53 smoothly so as to define a curved passage for the exhaust gas.The water passage W2 defined by the second port member 53 and the secondcover member 54 includes a water inlet 59 on the lower side thereof anda water outlet 60 on the upper side thereof.

The shape of the water passage W2 of the independent exhaust port 16A isnow explained with reference to FIG. 8 to FIG. 10.

The water passage W2 is formed with lateral symmetry relative to a planeof symmetry P1 of the independent exhaust port 16A; immediately afterthe water inlet 59 the water passage W2 branches into two lines so as tosandwich the plane of symmetry P1 and the two lines merge againimmediately before the water outlet 60. To explain in more detail, thewater passage W2 extends linearly from the water inlet 59 along a lowerface of the downstream portion 58 (part a), moves therefrom to theupstream portion 55, extends in a semicircular shape around the head 30a of the exhaust valve 30 (part b), extends therefrom linearly upwardalong the stem 30 b of the exhaust valve 30 up to the vicinity of thelower end of the exhaust valve guide 40 (part c), extends therefromtoward the head 30 a of the exhaust valve 30 while bent in a zigzagshape (part d), returns therefrom back to the downstream portion 58, andextends toward the water outlet 60 while bent in a zigzag shape (parte).

The structure of the grouped exhaust port 16B is now explained in detailwith reference to FIG. 2 to FIG. 6.

The grouped exhaust port 16B includes a rectangular frame-shaped flange61, and by tightening a plurality of bolts 62 running through a flange11 a of the main evaporator 11 to the cylinder head 20 the mainevaporator 11 and the grouped exhaust port 16B are together secured tothe cylinder head 20 (see FIG. 2). The downstream end of a pressed sheetmaterial third port member 63 is welded to the flange 61 of the groupedexhaust port 16B, and four openings 63 a formed in the upstream end ofthe third port member 63 communicate with exits of the four independentexhaust ports 16A. The downstream end of a pressed sheet material fourthport member 64 is welded to an inner face of the third port member 63,and the upstream end of the fourth port member 64 is superimposed on thefour openings 63 a of the third port member 63 and welded. The exhaustgases discharged from the four independent exhaust ports 16A aretherefore merged in the grouped exhaust port 16B, and guided evenly tothe main evaporator 11.

Water passages W1, which are formed from a pipe material, are disposedin a space surrounded by the third port member 63 and the fourth portmember 64 of the grouped exhaust port 16B. Since the water passages W1have a symmetrical structure relative to a plane of symmetry P2, FIG. 4to FIG. 6, FIG. 11A, and FIG. 11B show the water passage W1 on one sideof the plane of symmetry P2. The water passage W1 has a first linepassing through the independent exhaust port 16A(1) on the side close tothe plane of symmetry P2 and a second line passing through theindependent exhaust port 16A(2) on the side far from the plane ofsymmetry P2.

That is, the water passage W1 starting at a water inlet 65 provided onan end portion of the flange 61 extends linearly along an inner face ofthe fourth port member 64 (part f), and extends linearly therefrom alongan inner face of the third port member 63 (part g). A coupling 66 isprovided in the part g, and the water inlet 59 of the independentexhaust port 16A(1) is connected to this coupling 66. The water passageW1 extending from a coupling 67 to which the water outlet 60 of theindependent exhaust port 16A(1) is connected extends linearly along theinner face of the third port member 63 (part h), extends therefrom alongthe inner face of the third port member 63 in a zigzag shape (part i),extends linearly therefrom along the inner face of the third port member63 (part j), turns downward through 90°, and communicates with the wateroutlet 68. The water outlet 68 communicates with an intermediate portionof the main evaporator 11 via a connecting pipe 106, which will bedescribed later.

The water passage W1 extending through the coupling 66 further extendsalong the inner face of the third port member 63 in a zigzag shape (partk), extends linearly along the inner face of the fourth port member 64(part m), turns through 90°, extends linearly (part n), further turnsthrough 90°, extends linearly along the inner face of the third portmember 63 (part o), and is connected to the water inlet 59 of theindependent exhaust port 16A(2) via a coupling 69 provided therein. Acoupling 70 to which the water outlet 60 of the independent exhaust port16A(2) is connected merges with the part j of the water passage W1.

The structure of the main evaporator 11 is now explained in detail withreference to FIG. 12 to FIG. 21.

The main evaporator 11, which communicates with the downstream side ofthe auxiliary evaporator 17, has a casing 81 fixed to its flange 11 a,the cross section of the casing 81 being substantially rectangular, andan exhaust exit 11 b communicating with an exhaust pipe 82 (see FIG. 13)is formed on a lower face of the casing 81. A large number of thin metalheat transfer plates 83 are disposed parallel to each other at apredetermined pitch within the casing 81. An exhaust gas purificationcatalyst for cleaning up the exhaust gas is supported on the surface ofall of the heat transfer plates 83.

As is clear from FIG. 16, the heat transfer plate 83 is formed from afirst heat transfer plate 83(1) and a second heat transfer plate 83(2)having plane-symmetric concavoconvex portions, and they are alternatelysuperimposed. The first heat transfer plate 83(1) and the second heattransfer plate 83(2) thus make contact and are brazed to each other atabutment sections 84 and 85, and a partition wall 86 for blocking thecirculation of exhaust gas is formed in this section.

The partition wall 86 is arranged in the shape shown in FIG. 12, andforms a bent exhaust gas passage between adjacent heat transfer plates83. The exhaust gas passage is formed from a first exhaust gas passage87, a second exhaust gas passage 88, and a third exhaust gas passage 89,the first exhaust gas passage 87 communicating with the downstream endof the auxiliary evaporator 17 and extending linearly in a directionaway from the cylinder head 20, the second exhaust gas passage 88bending through 180° at the downstream end of the first exhaust gaspassage 87 and extending linearly toward the cylinder head 20, and thethird exhaust gas passage 89 bending through 180° at the downstream endof the second exhaust gas passage 88, extending in a direction away fromthe cylinder head 20, further bending through 90°, and extendingdownward so as to form an overall L-shape. An exhaust gas-combiningsection 81 a formed within the casing 81, which the downstream end ofthe third exhaust gas passage 89 faces, is connected to the exhaust pipe82 via the exhaust exit 11 b. Furthermore, a gap 86 a is provided bycutting away a portion of the partition wall 86 of the heat transferplate 83 on the high temperature side of the first, second, and thirdexhaust gas passages 87, 88, and 89, thereby blocking heat transfer froma high temperature portion to a low temperature portion of the heattransfer plates 83 and enabling the high temperature portion and the lowtemperature portion to be maintained at desired temperatures.

A large number of pipe members 90, through which water circulates, runthrough all the heat transfer plates 83 and are joined integrallythereto by brazing so that heat transfer is possible therebetween.

As is clear by referring additionally to FIG. 12, FIG. 15, and FIG. 19,an oxygen concentration sensor 91 is mounted on the middle of the lowerface of the main evaporator 11, and a detection portion 91 a at theextremity thereof faces the first exhaust gas passage 87. Provided onthe lower face of the main evaporator 11 on which the oxygenconcentration sensor 91 is mounted is an oxygen concentration sensorcooling portion 92, which is partitioned off beneath the first exhaustgas passage 87 via the partition wall 86. A flat upper face of theoxygen concentration sensor cooling portion 92 faces the first exhaustgas passage 87 via the partition wall 86, and a lower face thereof facesthe atmosphere via the casing 81. The oxygen concentration sensorcooling portion 92 includes a plurality of pipe members 93, which runthrough the heat transfer plates 83 and are joined thereto by brazing.

As is most clearly shown in FIG. 15, left and right headers 96L and 96Rare provided at longitudinally opposite ends of the casing 81 of themain evaporator 11, the left and right headers 96L and 96R being formedby integrally connecting inner plates 94 and outer plates 95 with apredetermined gap therebetween. Each of the headers 96L, 96R has theinner plate 94 thereof superimposed on the heat transfer plate 83 thatis layered on the outermost side. A water inlet pipe 97 communicatingwith the downstream side of the supply pump 15 runs through a rear faceof the casing 81 of the main evaporator 11, reaches the outer face ofthe outer plate 95 of the left-hand (when facing the cylinder head 20)header 96L, and is connected via a bifurcated coupling 98 to two of thepipe members 90 positioned at the downstream end of the third exhaustgas passage 89.

These two pipe members 90 form the beginning of two lines of waterpassages W3, and adjacent pipe members 90 of each line are sequentiallyconnected via U-shaped couplings 99 in the left and right headers 96Land 96R, thus forming the water passages W3 in a zigzag shape. As isclear from FIG. 22, the direction of flow of water in the water passagesW3 is opposite to the direction of flow of exhaust gas, which is in thedirection first exhaust gas passage 87→second exhaust gas passage88→third exhaust gas passage 89, that is, the flow of water is from thethird exhaust gas passage 89 to the first exhaust gas passage 87 via thesecond exhaust gas passage 88. That is, the exhaust gas and the waterhave a countercurrent arrangement.

As is clear from FIG. 12, the density of the pipe members 90 is the mostsparse in the first exhaust gas passage 87, which is on the upstreamside of the flow of exhaust gas, moderate in the second exhaust gaspassage 88, which is in the middle, and the most dense in the thirdexhaust gas passage 89, which is on the downstream side.

As is clear from FIG. 15, a water inlet pipe 100 communicating with thedownstream side of the supply pump 15 runs through a rear face of thecasing 81 of the main evaporator 11 and reaches an outer face of theouter plate 95 of the left-hand (when facing the cylinder head 20)header 96L, and is connected to two of the pipe members 93 via abifurcated coupling 101. These two pipe members 93 form the beginning oftwo lines of water passages W4, and adjacent pipe members 93 of eachline are connected via U-shaped couplings 102 in the left and rightheaders 96L and 96R and via five couplings 103 in a space surroundingthe oxygen concentration sensor 91, thus forming the water passages W4in a zigzag shape. The downstream ends of the two line water passages W4communicate via couplings 104 and connecting pipes 105 with the waterinlets 65 (see FIG. 5) of the auxiliary evaporator 17 formed within theflanges 11 a and 61.

As shown in FIG. 17, FIG. 18, and FIG. 21, the two connecting pipes 106communicating with the water outlets of the water passages W2 of theauxiliary evaporator 17 extend to the exterior of the casing 81 throughthe outside of the headers 96L and 96R, bend through 180°, re-enter theinterior of the casing 81, and are connected to the pipe members 90 ofthe cooling water passages W3 via bifurcated couplings 107 provided inthe headers 96L and 96R. The position of the pipe members 90 connectedto the connecting pipes 106 is in the vicinity of the upstream end ofthe second exhaust gas passage 88 as shown by the reference numerals90(1) and 90(2) in FIG. 22.

As shown in FIG. 21, in the right-hand header 96R, the two pipe members90 (shown by the reference numerals 90(3) and 90(4) in FIG. 22)positioned at the downstream end of the water passages W3 are connectedvia a bifurcated coupling 108 to a water outlet pipe 109 thatcommunicates with the expander 12.

The operation of the embodiment of the present invention having theabove-mentioned arrangement is now explained.

In FIG. 1, a portion of the water discharged from the supply pump 15 ofthe Rankine cycle system is supplied to the main evaporator 11, which isprovided downstream of the exhaust port 16 of the internal combustionengine E, and the rest of the water discharged from the supply pump 15passes through the auxiliary evaporator 17 provided on the outerperiphery of the exhaust port 16 and merges into the main evaporator 11at a predetermined position.

The operation in the main evaporator 11 is first explained. A portion ofthe low temperature water discharged from the supply pump 15 flows tothe left header 96L of the casing 81 of the main evaporator 11 via thewater inlet pipe 97 (see FIG. 15), and the flow is divided into the twolines of water passages W3 via the coupling 98. Each of the waterpassages W3 is formed from the large number of pipe members 90 connectedin a zigzag shape, and carries out heat exchange with the exhaust gaspassing through the gaps between the large number of heat transferplates 83, through which the pipe members 90 run, thereby depriving theexhaust gas of thermal energy and increasing in temperature. The twopipe members 90 at the downstream end of the two lines of water passagesW3 are merged with the water outlet pipe 109 (see FIG. 21) via thecoupling 108. The water is heated and turns into high temperature, highpressure steam while flowing through the water passages W3, and issupplied to the expander 12.

Since the heat of the exhaust gas is transferred from the large numberof heat transfer plates 83, which have a large surface area and arearranged at a small pitch, to the water flowing through the large numberof pipe members 90, it is possible to ensure that there is a sufficientarea of heat exchange between the exhaust gas and the water.Accordingly, even when the flow rate of the exhaust gas is reduced, thatis, when the cross-sectional area of the exhaust gas flow path in themain evaporator 11 is increased, sufficient heat exchange efficiency canbe obtained, and suppressing an increase in the back pressure of theexhaust passage can prevent any decrease in the output of the internalcombustion engine E. Furthermore, when pressing the heat transfer plates83, the partition wall 86 can be provided in any shape by forming onlythe abutment sections 84 and 85, and the first to third exhaust gaspassages 87, 88, and 89, which are bent, can be formed without employingany special component for providing the partition wall 86.

Moreover, as is clear from FIG. 22 and FIG. 23, whereas the exhaust gasflows from the first exhaust gas passage 87 to the third exhaust gaspassage 89 via the second exhaust gas passage 88, water within the waterpassages W3 flows from the third exhaust gas passage 89 to the firstexhaust gas passage 87 via the second exhaust gas passage 88 so as tooppose the direction of flow of the exhaust gas, thereby ensuring thatthere is sufficient temperature difference between the water and theexhaust gas along the whole length of the water passages W3 andimproving the heat exchange efficiency of the main evaporator 11.

Furthermore, since the density of the pipe members 90 is low in thefirst exhaust gas passage 87, which is on the upstream side of the flowof the exhaust gas, and the density of the pipe members 90 graduallyincreases therefrom toward the third exhaust gas passage 89, which is onthe downstream side, by reducing the density of the pipe members 90 inthe upstream section where the exhaust gas has a high temperature and alarge volume and the flow rate is high it is possible to minimize thepressure loss due to impingement of the exhaust gas on the pipe members90, and by increasing the density of the pipe members 90 in thedownstream section where the exhaust gas has a low temperature and asmall volume and the flow rate is low it is possible to ensure thatthere is sufficient contact between the exhaust gas and the pipe members90 and improve the heat exchange efficiency.

Moreover, since the exhaust gas purification catalyst is supported onthe heat transfer plates 83, which have a large surface area, it ispossible to ensure that the exhaust gas makes sufficient contact withthe exhaust gas purification catalyst, thereby cleaning the exhaust gaseffectively.

The rest of the low temperature water discharged from the supply pump 15enters the interior of the left-hand header 96L of the casing 81 of themain evaporator 11 via the water inlet pipe 100 (see FIG. 15), and theflow thereof is divided into the two lines of water passages W4 via thecoupling 101. Water that has flowed in a zigzag shape through theinterior of the pipe members 93 forming each of the water passages W4 isfirst merged in the H-shaped coupling 103 in the vicinity of the oxygenconcentration sensor 91, is then divided again, further flows in azigzag shape through the interior of the pipe members 93, then flowsfrom the left and right headers 96L and 96R through the couplings 104,the connecting pipes 105, and the water inlets 65, and is then suppliedto the auxiliary evaporator 17.

In this way, since the surroundings of the oxygen concentration sensor91, which passes through the oxygen concentration sensor cooling portion92, are cooled by the low temperature water flowing through the waterpassages W4, the heat of the high temperature exhaust gas flowingthrough the first exhaust gas passage 87, which the detection portion 91a of the oxygen concentration sensor 91 faces, can be prevented fromescaping to the outside of the main evaporator 11 via the oxygenconcentration sensor 91, thereby improving the efficiency of recovery ofwaste heat of the internal combustion engine E.

Furthermore, since the first exhaust gas passage 87 and the secondexhaust gas passage 88, which are positioned on the upstream side of theflow of exhaust gas and through which the high temperature exhaust gasflows, are disposed in a radially inner portion of the main evaporator11, the third exhaust gas passage 89, which is positioned on thedownstream side of the flow of exhaust gas and to which water having thelowest temperature is supplied, is disposed in a radially outer portionof the main evaporator 11, and the oxygen concentration sensor coolingportion 92, to which water having the lowest temperature is supplied, isdisposed in a radially outer portion of the main evaporator 11, that is,since the outsides of the first exhaust gas passage 87 and the secondexhaust gas passage 88, which reach a high temperature due to thepassage of high temperature exhaust gas, are surrounded by the thirdexhaust gas passage 89 and the oxygen concentration sensor coolingportion 92, which reach a low temperature due to the passage of lowtemperature water, it is possible to minimize the dissipation of thermalenergy to the outside of the main evaporator 11, thereby improving thewaste heat recovery efficiency.

A gap that maintains an air layer is formed between the inner peripheryof the casing 81 and the outer periphery of the heat transfer plates 83,and the heat insulating effect of this air layer can further reduce thedissipation of thermal energy to the outside of the main evaporator 11.

The operation in the auxiliary evaporator 17 is now explained. In FIG.11A and FIG. 11B, water discharged from the oxygen concentration sensorcooling portion 92 flows into the water passage W1 from the water inlet65 of the grouped exhaust port 16B and the flow is divided into thefirst line and the second line. The first line shown in FIG. 11A has aroute that reaches the water outlet 68 via the part f and the part g ofthe water passage W1, the coupling 66, the water passage W2 of theindependent exhaust port 16A(1), the coupling 67, and the part h, thepart i, and the part j of the water passage W1. On the other hand, thesecond line shown in FIG. 11B has a route that reaches the water outlet68 via the part f, the part g, the part k, the part m, the part n, andthe part o of the water passage W1, the coupling 69, the water passageW2 of the independent exhaust port 16A(2), and the part j of the waterpassage W1. Since in the first line the first half of the water passageW1 is short and the second half thereof is long, and in the second linethe first half of the water passage W1 is long and the second halfthereof is short, the overall length of the water passage W1 in the twolines is equalized, thus making the amount supplied substantially equal,preventing an imbalance in the waste heat recovery, and improving theheat exchange efficiency.

As shown in FIG. 7 to FIG. 10, the structures of the water passages W2provided in the two independent exhaust ports 16A(1) and 16A(2) areidentical, and water supplied from the water inlet 59 branches so as tosandwich the plane of symmetry P1, passes through the part a, the partb, the part c, the part d, and the part e, is merged, and is thendischarged via the water outlet 60.

In this way, since the auxiliary evaporator 17 is arranged so that thesurroundings of the exhaust port 16, which reach a high temperature dueto the passage of exhaust gas, are surrounded by the water passages W1and W2, the exhaust gas heat dissipated from the exhaust port 16 via thecylinder head 20 can be recovered effectively as high temperature, highpressure steam. In particular, since the water supplied to the waterpassages W1 and W2 is comparatively low temperature water that has onlypassed through the oxygen concentration sensor cooling portion 92 afterbeing discharged from the supply pump 15, the surroundings of theexhaust port 16 can be cooled effectively, and high temperature, highpressure steam can be generated, thus enhancing the waste heat recoveryeffect of the internal combustion engine E. Furthermore, although theheat of exhaust gas easily escapes to the outside via the exhaust valve30, intensive cooling, with low temperature water, of the section thatrequires cooling of the internal combustion engine E, that is, theexhaust valve seat 29, with which the head 30 a of the exhaust valve 30makes contact, and the vicinity of the exhaust valve guide 40, withwhich the stem 30 b of the exhaust valve 30 makes contact, enables theescape of heat via the exhaust valve 30 to be suppressed, thus furtherenhancing the waste heat recovery effect, and enables thermal expansionof the exhaust valve 30, the exhaust valve seat 29, and the exhaustvalve guide 40, etc. to be suppressed, thus maintaining dimensional andpositional precision and thereby maintaining desired functions thereof.

Water that has passed through the auxiliary evaporator 17 passes fromthe connecting pipes 106 (see FIG. 17 and FIG. 18) through the couplings107 (see FIG. 20) provided in the left and right headers 96L and 96R,and is merged in the pipe members 90 of the second exhaust gas passage88 of the main evaporator 11. In this arrangement, by making, in themerging section, the temperature of water passing through the waterpassages W3 on the main evaporator 11 side substantially equal to thetemperature of water supplied from the auxiliary evaporator 17, thewaste heat recovery effect can be further improved. This control ofwater temperature can be carried out by regulating the flow rate ratiowhen splitting the flow of water discharged from the supply pump 15 intothe main evaporator 1 1 side and the auxiliary evaporator 17 side.

Although an embodiment of the present invention is explained in detailabove, the present invention can be modified in a variety of wayswithout departing from the spirit and scope of the present invention.

For example, in the embodiment the heat exchanger is exemplified by themain evaporator 11, but the heat exchanger of the present invention isnot limited to an evaporator.

Furthermore, in the embodiment water is illustrated as the heat medium,but the heat medium of the present invention is not limited to water.

INDUSTRIAL APPLICABILITY

Although the present invention can be suitably applied to an evaporatorfor a Rankine cycle system and, in particular, to an evaporator for aRankine cycle system that recovers the thermal energy of the exhaust gasof an internal combustion engine of an automobile and converts it intomechanical energy, the present invention can also be applied to a heatexchanger for any purpose.

1. A heat exchanger for recovering, with a heat medium flowing through aheat medium passage (W3), the thermal energy of a high temperature fluidflowing through the interior of a fluid passage (87, 88, 89) extendingfrom a heat source (24), characterized in that the fluid passage (87,88, 89) is formed by arranging a large number of heat transfer plates(83) at intervals from each other and partitioning the gaps betweenadjacent heat transfer plates (83) using a partition wall (86) that isformed integrally with the heat transfer plates (83), and the heatmedium passage (W3) is formed from a large number of pipe members (90)running through the heat transfer plates (83) and being connected in azigzag shape.
 2. The heat exchanger according to claim 1, wherein thepacking density of the pipe members (90) disposed on the upstream sideof the fluid passage (87, 88, 89) is sparse and the packing density onthe downstream side of the fluid passage (87, 88, 89) is dense.
 3. Theheat exchanger according to either claim 1 or claim 2, wherein the heatsource is a combustion chamber (24) of an internal combustion engine(E), the high temperature fluid is exhaust gas discharged from thecombustion chamber (24), and the heat transfer plates (83) support anexhaust gas purification catalyst.